Highly-selective signal reception



Oct. 30, 1928.

. R. A. HEISING HIGHLY SELECTIVE SIGNAL RECBPHON Filed Dec. 27, 192s fiy/ x lm enfar Raymond A. flelsmy by W Patented Oct. 30, 1928.

UNITED STATES PATENT OFFICE.

RAYMOND A. HEISING, 0]? MILLBURN, NEW JERSEY, ASSIGNOR TO'WES'IERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y.,' A CORPORATION OF NEW YORK.

HIGHLY-SELECTIVE SIGNAL RECEPTION.

Application filed December 27, 1923. Serial No. 682,857.

The invention relates to improvements in signaling with the object of increasing selectivity.

An object of the invention is to provide .ing in wave form to the difi'erential of a wave produced by a detecting device.

A further object is to provide for greater selectivity in radio reception, whereby signaling channels may be operated upon closely' adjacent frequencies.

In one form of apparatus described herein for illustrating the invention, incoming waves are selected by means. o f'a highly selective band-pass filter designed to transmit a band of frequencies relatively narrow as compared to selective circuits hitherto used. The wave transmitted through the filter is impressed upon a vacuum tube detector. Owing to the high timeconjstant'of the band filter, the wave form of the signal will be distorted. In order to correct this, there'is employed a difl'erentiator circuit,' which. in its simplest form, consists of a high inductance in the plate circuit of the. detectorand a thermionic relay associated with the inductance by connecting its input terminals thereacross'.

Modifiedforms involve a highly selective tuned circuit and a regenerative circuit as selective elements ofhigh time constant and loW damping constant.

The invention will be more particularly described inconnection with the accompanyin drawings wherein Fig.1 is a circuit diagram of a receiving system embodying the invention Fig.2 is a v iagram of the form of s1gnaling wave transmitted from 'a distant transmitting station Fig. 3 is a graphical illustration of'the form of wave produced at the receiving'station by the detector;---ancl Fig. 42 is a aph illustrative oft-he form nf waveep'phed to the input circuit on! vacuum tube relay which constitutes an elementof the differentiator circuit.

Fig. 5 is a fragmentary circuit diagram which may be substituted for that part of Fig. 1 to the left of the dotted line -XX. F ig.- 6 is another modified formof circuit which involves a regenerative circuit for the selective element of high time constant and low damping constant.

In Fig. 1, waves received by an antenna 1 are transmitted through a band filter 2 designed to transmit Waves of a narrow'band of frequencies and to suppress waves of frequencies being without the band. A circuit v j 2 is'regarded as the equivalent of any one of a number of highly selective circuits adapted to transmit narrow rangesof frequencies, and may consist of several groups of'sections having thermionic amplifiers between the groups or may consist of such a selective system of circuits such as is shown in the patent to Alexanderson N0. 1,173,07 9, February 22, 1916. The output terminal of the selective circuit 2 is connected to a vacu um tube detector 3 having the usual grid leak resistance 4 shunted by condenser 5. The cathode of the tube 3'is connected to the anode through the usual plate orB-battery 6 anda coil 7 of high inductance. Across the terminals of the coil 7 is-connected the grid-cathode circuit of a vacuum tube relay 8 in circuit with which may be provided the usual negative grid bias" battery 9. The source 11 isthe usual anode-cathode source for the'tube 8." The battery 9 may, if desired, be adjusted to suchlvaluethatlittle or no space current will fiovv'in the anode-cathode circuit ofthe tube 8, but may be adjusted to any value such that the current flowing in the anocle cathode circuit is below that necessary to actuate or retain actuated the receiving relay or sounder 10. The relay 10' typifies any suitable for controlling receiving apparatus or causing signals to be indicated. i The operation of the system of Fig. 1, will be described by reference to the graphs of Figs. 2, 3 and 4. In Fig. 2, the elements a represent groups of high frequency waves a sent out from a transmitter and corresponding to dots and the element 6 represents a longer group of waves corre= spending to adash. Owin a; the sesame seitcctive'eimats e, the snags element impressed upon the input circuit of the detector 3 as a result of the impression and removal of a group of high frequency waves a, will be a slowly rising and subsequently slowly falling curve 0 as shown in Fig. 3. A long group of waves corresponding to a dash b will produce a longer rising value of potential upon the input of the tube 8 as shown at d with a subsequently falling portion 6. The voltage across the inductance 7 will be proportional to the first differential of the curve 0, (l, c, or in other words, the amplitude of this voltage will be proportional to the rate of change with respect to the time of the amplitude of the curve 0, (Z, c. The wave form of this differential curve is indicated in Fig. l, with the sign reversed, that is, with the negative pulses plotted above the axis. Upon inspection, it appears that the wave form of the curve A, A, B in Fig. 4 is a very fair approximation of the wave form a, a, 72, illustrated in Fig. 2. Consequently, the distortion produced by the highly selective filter circuit 2 of a high frequency receiving system similar to the arrangement of Fig. 1 may be very largely corrected for by means of the differentiator circuit described and illustrated.

The expression high time constant. as ap-.

plied to the selective circuit 2 is used with reference to that property of such a circuit by virtue of which upon the application of a sustained continuous alternating voltage to the input circuit the elapse of a substantial period of time covering a considerable number of cycles, is required before the voltage at the output terminals builds up approximately to its maximum value. This is indicated in Fig. 3 by the dotted extensions 00, 00, of the solid line curves showing that the integrated output voltage would continue to build up gradually to a maximum value over the time much longer than that of a signal element if a sustained alternating voltage were continuously applied. Likewise, the integrated output voltage would decrease for an equally long period of time if a sustained alternating current, having been applied to the imput circuit until the steady state condition, was reached, were removed.

The mode of operation of the system of Fig. 1 will be obvious to those skilled in the art and consequently needs no greatly detailed description. One feature worthy of comment is the action of the high inductance 7 when connected between the space discharge-relays 3 and 8. The output circuit of the relay 3 is of fairly high value of impedance and the input circuit of the relay 8 will in general be of a high value of impedance or an extremely high value when the negative grid polarizing battery 9 is provided. The input im edance of the relay 8 at low frequencies sue as .Morse frequencies may amount to millions of ohms so that the voltage produced across the term1- nals of the inductance 7 by changing the 1mpedance of the tube 3 are very effectively emintermediate frequency or frequencies in.

"double detection systems. For radio work it is contemplated that the received waves may be of the order of frequency of upward of 1,000,000 cycles per second yet frequencies as low asand lower than 30,000 cycles per second are contemplated.

In Fig. 5 the circuit 11 is made of extremely high selectivity, high time constant, and low damping constant. This circuit takes the place of the circuit 2 of Fig. 1.

In Figure 6, the tube 3 has associated with it such electrical elements as are necessary to constitute a regenerative circuit. Tuning may be accomplished by varying inductances 12 and 13 and keeping capacity 14 constant or by adjusting capacity 14 and keeping inductances 12 and 13 constant. Resistance 15 may be adjusted to any suitable value. lVhen properly adjusted such a regenerative circuit has a high time constant and low damping constant. The detected and distorted signal waves are applied to coil 7 the inductance of which constitutes one element of the dilferentiator circuit as in the arrangement of Figure l.

The various novel features believed to be inherent in the-invention are set forth in the appended claims.

What is claimed is: V

1. The combination in a radio telegraph receiving system of a highly selective narrow band selecting circuit having a high time constant feeding into a detector and a circuit connected to said detector having the property of increasing the steepness of the wave fronts of the signal elements to counteract the distorting properties of said highly selective circuit.

2. A circuit for detecting impressed waves and means for deriving from the detected waves wave components representing the rate of change of amplitude of the impressed waves comprising a space discharge relay having in its anode-cathode or plate circuit an element of high electrical inertia in combination with a space discharge relay of high input impedance and meansto im- The waves arriving at the in press on its cathode-grid or input circuit the voltage waves developed across said element of high impedance.

3. A wave selecting, detecting, correcting and indicating system comprising in tandem arrangement a selective circuit having a high time constant, a space discharge detector having a control element with a leak path of high resistance attached thereto, a device of high electrical inertia in the output circuit of the detector, having the property of developing voltage waves compensated for the distortion produced by said selective circuit, a space discharge relay, means to impress across its input terminals compensated voltage waves so developed, and an indicator connected to said space dis charge relay.

4:. A wave selecting, detecting, and indicating system including in tandem arrangement in the order named a highly selective circuit, a detector, an inductance in the output circuit of said detector, having the property of restoring the detected waves in substantial amount to approach the form of the envelope of the waves existing before detection, a voltage controlled relay of high input impedance and means to impress on the input of said relay the detected waves of restored form.

5. In combination a highly selective circuit, an integrating detector, and a differentiator circuit consisting of a high inductance in the plate circuit of the detector and a thermionic relay associated with the inductance by connecting its input terminals thereacross, said elements being connected in circuit in tandem in the order named, said diflerentiator circuit acting to reform the Waves traversing the circuit to oppose the distortion introduced by said highly selective circuit.

6. The methodof receiving a signal element which consists in producing a current wave of amplitude varying approximately as the time summation of the energy of the waves comprising the signal element and producing under the control of said wave, a wave of instantaneous amplitudes proportional to instantaneous rates of change of said current waves.

7. In a high frequency wave receiving system a selecting and detecting circuit including a space discharge relay, said relay being followed in tandem relation by a difl'erentiator circuit consisting of a high inductance in the plate circuit of said discharge relay, and a thermionic relay associated with the inductance by connecting its input terminals thereacross.

In witness whereof, I hereunto subscribe my name this 22nd day of December A. D.,

RAYMOND A. HEISING. 

